Etching to reduce line wiggling

ABSTRACT

A method for reducing wiggling in a line includes forming a first patterning layer over a metal feature and depositing a first mask layer over the first patterning layer. The first mask layer is patterned to form a first set of one or more openings therein and then thinned. The pattern of the first mask layer is transferred to the first patterning layer to form a second set of one or more openings therein. The first patterning layer is etched to widen the second set of one or more openings. The first patterning layer may be comprised of silicon or an oxide material. The openings in the first patterning layer may be widened while a mask layer is over the first patterning layer.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims priority to U.S. Provisional Patent Application No. 62/552,490, entitled “Etching to Reduce Line Wiggling,” filed on Aug. 31, 2017, which application is hereby incorporated herein by reference.

BACKGROUND

In order to form integrated circuits on wafers, lithography process is used. A typical lithography process involves applying a photo resist, and defining patterns on the photo resist. The patterns in the patterned photo resist are defined in a lithography mask, and are defined either by the transparent portions or by the opaque portions in the lithography mask. The patterns in the patterned photo resist are then transferred to the underlying features through an etching step, wherein the patterned photo resist is used as an etching mask. After the etching step, the patterned photo resist is removed.

With the increasing down-scaling of integrated circuits, high aspect ratio stacking of layers used in photo patterning techniques can lead to poor wiggling resistance during pattern transfer to an amorphous silicon substrate. Line wiggling can, in turn, lead to pattern defects. Pattern defects and line wiggling can result in in breaking metal pattern lines and cause the pattern to fail.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1 through 11 illustrate intermediate steps of a self-aligned double patterning method of forming a metal line having a reduced wiggle, in accordance with some embodiments.

FIGS. 12 through 21 illustrate an intermediate step of a double patterning method of forming a metal line having a reduced wiggle, in accordance with some embodiments.

FIG. 22 illustrates a top-down view of a series of metal lines having reduced wiggle which are formed according to a pattern, in accordance with some embodiments.

FIGS. 23-24 illustrate intermediate steps of a method for forming semiconductor strips in a semiconductor substrate, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Embodiments of the present invention provide a method of producing metal lines which reduce the amount of line wiggle in the formation of metal lines. Line wiggle occurs when a pattern defined by a high aspect ratio, height-to-width, of a mask layer is transferred onto an pattern layer underneath which is used to define openings corresponding to the metal lines. Line wiggle in the mask layer is transferred to the pattern layer and line wiggle in the pattern layer is transferred to the line layer. Embodiments discussed below reduce the height-to-width aspect ratio of another pattern layer which is used to define the mask layer, resulting in a mask layer with less line wiggle which transfers to the subsequent layers to provide a line layer also with less wiggle. As such, the metal lines will also have less line wiggle. Embodiments can be used to provide metal lines resulting from multiple patterning techniques, such as a self-aligned double patterning (SADP) or two-patterning-two-etching (2P2E) techniques. Intermediate stages of forming a metal line using these techniques are illustrated in accordance with example embodiments.

FIGS. 1 through 11 illustrate cross-sectional views of intermediate stages in the formation of features in a target layer in accordance with some embodiments using a self-aligned double patterning process. FIG. 1 illustrates device 100, which includes substrate 10 and the overlying layers. Substrate 10 may be formed of a semiconductor material such as silicon, silicon germanium, or the like. In some embodiments, substrate 10 is a crystalline semiconductor substrate such as a crystalline silicon substrate, a crystalline silicon carbon substrate, a crystalline silicon germanium substrate, a III-V compound semiconductor substrate, or the like. In an embodiment the substrate 10 may comprise bulk silicon, doped or undoped, or an active layer of a silicon-on-insulator (SOI) substrate. Generally, an SOI substrate comprises a layer of a semiconductor material such as silicon, germanium, silicon germanium, or combinations thereof, such as silicon germanium on insulator (SGOI). Other substrates that may be used include multi-layered substrates, gradient substrates, or hybrid orientation substrates.

Devices (e.g., transistor 11) may include both active devices and passive devices and are formed at a top surface of or within substrate 10. Active devices may comprise a wide variety of active devices such as transistors and the like and passive devices may comprise devices such as capacitors, resistors, inductors and the like that together may be used to generate the desired structural and functional parts of the design. The active devices and passive devices may be formed using any suitable methods either within or else on the substrate 10. For example, one device may be transistor 11, which includes a gate electrode 12, gate spacers 13, and source/drain regions 14. Gate and source/drain contacts 15 can be used to electrically couple to transistor 11. Transistor 11 may be a fin or planar field effect transistor (FET), and may be an n-type or p-type transistor or part of a complimentary metal-oxide semiconductor (CMOS). A dielectric layer 16 may include one or more layers of dielectric material in which contact structures 15 are electrically coupled to active devices and passive devices.

Metallization structure 21 is formed over substrate 10. Metallization structure 21 includes a dielectric layer 22 with conductive features 24 formed therein. Metallization structure 21 may be a layer of an interconnect or redistribution structure which may have additional layers. For example, metallization structure 21 may include an dielectric layer 22, such as an Inter-Metal Dielectric (IMD) layer or an Inter-Layer Dielectric (ILD) layer, which may include a dielectric material having a low dielectric constant (k value) lower than 3.8, lower than about 3.0, or lower than about 2.5, for example, and conductive features 24. The dielectric layer 22 of the metallization structure 21 may be formed of phosphosilicate glass (PSG), borosilicate glass (BSG), boron-doped phosphosilicate glass (BPSG), fluorine-doped silicate glass (FSG), tetraethyl orthosilicate (TEOS), Black Diamond (a registered trademark of Applied Materials Inc.), a carbon-containing low-k dielectric material, Hydrogen SilsesQuioxane (HSQ), MethylSilsesQuioxane (MSQ), or the like.

Metallization structure 21 (including one or more layers) is formed over the substrate 10 and the devices and is designed to connect the various devices to form functional circuitry for the circuit design. In an embodiment, the metallization structure 21 is formed of alternating layers of dielectric and conductive material and may be formed through any suitable process (such as deposition, damascene, dual damascene, etc.). In an embodiment there may be one to four layers of metallization separated from the substrate 10 by at least one interlayer dielectric layer (ILD), but the precise number of layers is dependent upon the design.

The conductive features 24 may include metal lines 24A and conductive vias 24B. Metal lines 24A may be formed in an upper portion of a layer of the metallization structure 21, and may be used for routing signals. Conductive vias 24B may extend through the dielectric layer 22 to contact underlying features. In an embodiment, the conductive features 24 may be a material such as copper formed using, e.g., a damascene or dual damascene process, whereby an opening is formed within the dielectric layer 22, the opening is filled and/or overfilled with a conductive material such as copper or tungsten, and a planarization process is performed to embed the conductive material 24 within the dielectric layer 22. However, any suitable material and any suitable process may be used to form the conductive features 24. In some embodiments, a barrier layer 25 may surround the conductive elements 24 and may be used as a diffusion barrier layer for preventing undesirable elements, such as copper, from diffusing into the surrounding dielectric material of the dielectric layer 22, for example, if the dielectric material of the dielectric layer 22 is a low-k dielectric material. In some embodiments, conductive features 24 may be contacts of a die.

Etch stop layer (ESL) 26 may comprise a dielectric material such as silicon carbide, silicon nitride, or the like. ESL 26 may be formed of a nitride, a silicon-carbon based material, a carbon-doped oxide, and/or combinations thereof. ESL 26 may be formed of a metallic material. The formation methods include Plasma Enhanced Chemical Vapor Deposition (PECVD) or other methods such as High-Density Plasma CVD (HDPCVD), Atomic Layer Deposition (ALD), low pressure CVD (LPCVD), physical vapor deposition (PVD), and the like. In accordance with some embodiments, ESL 26 is also used as a diffusion barrier layer for preventing undesirable elements, such as copper, from diffusing into the subsequently formed low-k dielectric layer. ESL 26 may include Carbon-Doped Oxide (CDO), carbon-incorporated silicon oxide (SiOC) or oxygen-Doped Carbide (ODC). ESL 26 may also be formed of Nitrogen-Doped silicon Carbide (NDC).

ESL 26 may comprise one or more distinct layers. In some embodiments, a first etch stop layer 26A is used to protect the underlying structures and provide a control point for a subsequent etching process through, for example, the second etch stop layer 26B. The first etch stop layer 26A may be deposited to a thickness of between about 15 Å and about 50 Å, such as about 30 Å. Other suitable thicknesses may be used.

Once the first etch stop layer 26A has been formed to cover the conductive elements 24, in some embodiments, a second etch stop layer 26B is formed over the first etch stop layer 26A. In some embodiments, the second etch stop layer 26B is formed of a material different than the first etch stop layer 26A. The material of the second etch stop layer 26B may be formed using a deposition process such as those listed above, and may be deposited to a thickness of between about 15 Å and about 35 Å, such as about 20 Å. However, any suitable process of formation and thickness may be utilized.

Further illustrated in FIG. 1 is dielectric layer 28 formed over etch stop layer 26. In accordance with some embodiments of the present disclosure, dielectric layer 28 is formed of a low-k dielectric material having a dielectric constant (k-value) lower than about 3.0, about 2.5, or even lower. Dielectric layer 28 may be formed using a material selected from the same group of candidate materials for forming dielectric layer 22. When selected from the same group of candidate materials, the materials of dielectric layers 22 and 28 may be the same or different from each other. In accordance with some embodiments, dielectric layer 28 is a silicon and carbon containing low-k dielectric layer. Dielectric layer 28 may also be referred to as a target layer, which will have openings formed therein according to a plurality of patterns and filled with metal lines and plugs, in accordance with embodiments of the present disclosure.

In some embodiments, over low-k dielectric layer 28 resides a mask 30. In some embodiments, mask 30 may be a dielectric hard mask and may be referred to as dielectric hard mask 30, which may be formed of silicon oxide (such as tetraethylorthosilicate (TEOS) oxide), Nitrogen-Free Anti-Reflective Coating (NFARC, which is an oxide), silicon carbide, silicon oxynitride, or the like. The formation methods include Plasma Enhance Chemical Vapor Deposition (PECVD), High-Density Plasma (HDP) deposition, or the like.

A mask 32 is formed over mask 30 or dielectric layer 28. In some embodiments mask 32 may be a hard mask and may also be referred to as hard mask 32. In some embodiments, hard mask 32 is a metal hard mask and may include one or more metals, such as titanium (Ti) or tantalum (Ta). In some embodiments, the metal of hard mask 32 may be in the form of a metal nitride such as titanium nitride (TiN) or tantalum nitride (TaN). In some embodiments, hard mask 32 may be formed of a non-metal nitride such as silicon nitride, an oxynitride such as silicon oxynitride, or the like. The formation methods of hard mask 32 include Physical Vapor Deposition (PVD), Radio Frequency PVD (RFPVD), Atomic Layer Deposition (ALD), or the like.

Dielectric mask 34 is formed over mask 32. In some embodiments, dielectric mask 34 may be a hard mask and may be referred to as dielectric hard mask 34. Dielectric hard mask 34 may be formed of a material selected from the same candidate material of dielectric hard mask 30, and may be formed using a method that is selected from the same group of candidate methods for forming dielectric hard mask 30. Dielectric hard masks 30 and 34 may be formed of the same material, or may comprise different materials. In some embodiments, dielectric hard mask 34 may be patterned after deposition to expose portions of the underlying hard mask 32. In such embodiments, the dielectric hard mask 34 may be used to etch the underlying target layer 28 to different depths.

Mandrel layer 36 is formed over dielectric hard mask 34. In some embodiments, mandrel layer 36 is formed of amorphous silicon or another material that has a high etching selectivity with the underlying dielectric hard mask 34. Mandrel layer 36 may have a thickness of about 300 to about 800 Å, such as about 500 Å. In some embodiments, Mandrel layer 36 may be a mandrel layer such as when using a self-aligned double patterning (SADP) technique. In some embodiments, Mandrel layer 36 may be a pattern mask layer to be used in a one-patterning-one-etching (1P1E) process. In accordance with some embodiments, such a pattern mask layer may be used in a two-patterning-two-etching (2P2E) process, wherein two neighboring openings (see, e.g., openings 78 and openings 80 of FIG. 19B) are formed in different lithography processes, so that neighboring openings may be located close to each other without incurring optical proximity effect. Additional patterning steps can be used on mandrel layer 36, such as three-patterning-three-etching (3P3E), and so on, or combinations of the techniques discussed above. Multiple patterning techniques are discussed below in conjunction with FIGS. 12-21.

After mandrel layer 36 is patterned (see layer 236 of FIG. 6), it will be used in a subsequent process as mandrels for a self-aligned patterning process which will result in patterning the target layer 28. When the height-to-width aspect ratio of the openings is high, the resulting metal features (e.g., metal lines) in the target layer 28 will wiggle, i.e., not be relatively straight, as a result of the etch process. Embodiments discussed herein control the height-to-width ratio of the openings which will be formed which result in metal features which have little to no wiggle.

Still referring to FIG. 1, a tri-layer is formed over the mandrel layer 36, the tri-layer comprising a bottom layer 38, a middle layer 40 over the bottom layer 38, and an upper layer 42 (also referred to as top layer) over the middle layer 40. In some embodiments, bottom layer 38 and upper layer 42 are formed of photo resists, which comprise organic materials. Middle layer 40 may comprise an inorganic material, which may be a carbide (such as silicon oxycarbide), a nitride (such as silicon nitride), an oxynitride (such as silicon oxynitride), an oxide (such as silicon oxide), or the like. Middle layer 40 has a high etching selectivity with relative to upper layer 42 and bottom layer 38, and hence upper layer 42 is used as an etching mask for the patterning of middle layer 40, and middle layer 40 is used as an etching mask for the patterning of bottom layer 38.

The thickness of the bottom layer 38 may be between about 250 and 1200 Å, such as about 500 Å. The thickness of the middle layer 40 may be between about 100 and 350 Å, such as about 260 Å. The thickness of the upper layer 42 may be between about 300 and 1000 Å, such as about 500 Å. Although example ranges and thicknesses of the layers are provided, other thicknesses of these layers can be used.

After the upper layer 42 is formed, upper layer 42 is patterned as illustrated in FIG. 1 using an acceptable photolithography technique. The patterned upper layer 42 includes openings 44 therein. In a top view of device 100, openings 44 may have shapes such as strips, round vias, or conductive patterns. Each of the openings 44 has a height-to-width ratio, h₁:w₁. In some embodiments, the height h₁ of the openings 44 corresponds to the thickness of the top layer 42 and the width w₁ of the openings 44 depends on the photolithography technique used to pattern the top layer 42. The width w₁ of the openings 44 may be between about 150 and 500 Å, such as about 300 Å. Other widths for the openings 44 can be used.

Next, referring to FIG. 2, in order to reduce the height-to-width ratio of the openings 44, the thickness of the upper layer 42 (and corresponding height h₁ of the openings 44 of FIG. 1) is reduced to a height h₁′. Any acceptable technique may be used to reduce the height of the openings 44 to create openings 144. For example an anisotropic etch may be performed which is selective to the material of the upper layer 42. In some embodiments, a CMP may be used to reduce the thickness of the upper layer 42 to create layer 142. The reduced height-to-width ratio, h₁′:w₁, may be between about 0.5 and 2.0, such as about 1.0. In some embodiments, the width w₁ may be changed to a width w₁′, for example, if the openings 44 of FIG. 1 are widened in the same process which reduces the height of the upper layer 42. In such embodiments, the resulting height-to-width ratio h₁′:w₁′ may be reduced over the ratio h₁:w₁ by an even greater extent.

The reduction of the height-to-width ratio of the openings 44 in the top layer 42 can be performed so that the subsequent etching of the middle layer 40 will have straighter etched lines than if the top layer was not thinned to change the height-to-width ratio of the openings 44.

Next, referring to FIG. 3, middle layer 40 is etched to form patterned middle layer 140, which may also be referred to as middle layer 140. Middle layer 40 is etched using the patterned upper layer 142 (FIG. 2) as an etching mask, so that the pattern of patterned upper layer 142 is transferred to middle layer 40 to create patterned middle layer 140. During the patterning of middle layer 140, upper layer 142 may be partially, or entirely, consumed. Etching the middle layer 40 may result in openings 46 in the middle layer 140 which have been extended from openings 144. Any suitable etching technique may be used, such as a wet or dry etch using an etchant which is selective to the middle layer 140 material.

Turning to FIG. 4, the bottom layer 38 is then etched to form patterned bottom layer 138, which may also be referred to as bottom layer 138. Bottom layer 38 is etched using the middle layer 140 as an etching mask, so that the pattern of middle layer 140 is transferred to bottom layer 38 to create a patterned bottom layer 138. The bottom layer 138 has openings 48 which have been extended from openings 46 (FIG. 3). Upper layer 142 will be fully consumed during the patterning of bottom layer 38 if it has not been fully consumed in the patterning of middle layer 140. Openings 48 may be tapered or may have vertical sidewalls, within process variations. Any suitable etching technique may be used, such as a wet or dry etch using an etchant which is selective to the material of bottom layer 138. For example, in some embodiments the etchant may be O₂ based or N₂/H₂ based etchant gas used in an etching chamber with other process gasses. Other suitable etchant gasses may be used. The bottom layer 38 etch process may be performed for an etch time t_(BT) between about 20 sec and about 60 sec, such as about 35 sec, at a pressure between about 3 mTorr and about 45 mTorr, such as about 8 mTorr, a temperature between about 15° C. and about 65° C., such as about 30° C., with a bias voltage applied at a power between about 100 V and about 500 V, such as about 300 V. Other environmental conditions and etch times may be used.

FIG. 5 illustrates an anisotropic etching of mandrel layer 36 of FIG. 4 to form patterned mandrel layer 136, which may also be referred to as mandrel layer 136. Mandrel layer 36 is etched using the patterned bottom layer 138 as an etching mask, so that the pattern of bottom layer 138 is transferred to mandrel layer 36 to create a patterned mandrel layer 136. The mandrel layer 136 has openings 50 which have been extended from openings 48 (FIG. 4). The etching technique may include a dry etch using a suitable etchant. In some embodiments, the etchant selected for etching the patterned mandrel layer 136 may be a fluorine free etchant, such as a chlorine based etchant. In other embodiments, other etchants may be used, including fluorine based etchants. Mask layer 34 under the patterned mandrel layer 136 may serve as an etch stop layer for the etching through of the mandrel layer 36. Openings 50 are formed as a result of the etching of the patterned mandrel layer 136. Openings 51 are the portions of the openings 50 in the patterned mandrel layer 136 which have a height h₂ and width w₂, where the height h₂ corresponds to the thickness of the layer 136 and the width w₂ corresponds to the width w₁, being approximately equal to the width w₁ or w₁′, within process variations. A resulting ratio of the height-to-width, h₂:w₂, may be about 0.8 to about 3.0, such as about 1.6.

The etch process illustrated by FIG. 5 may be performed for an etch time t_(BT) between about 15 sec and about 150 sec, such as about 80 sec, at a pressure between about 3 mTorr and about 80 mTorr, such as about 20 mTorr, and a temperature between about 25° C. and about 70° C., such as about 40° C. Other environmental conditions and etch times may be used.

FIG. 6 illustrates device 100 following a further etch of the patterned mandrel layer 136 to increase the width of the openings 50 in the patterned mandrel layer 136 and produce patterned mandrel layer 236. The openings 150 includes the entire opening through the remaining layers (i.e., patterned mandrel layer 236 and bottom layer 138). The openings 151 includes the portion of the openings 150 that are in the patterned mandrel layer 236. The further etch of the patterned mandrel layer 236 may be performed by wet etch using a suitable etchant selective to the material (e.g., amorphous silicon) of the patterned mandrel layer 236. The bottom layer 138 can protect the top portion of the patterned mandrel layer 236 such that the openings are widened without significantly altering the pattern of the patterned mandrel layer 236. In some embodiments, the resulting patterned mandrel layer 236 may have an inverted taper (the openings 151 being wider at the bottom than the top), depending on the etching techniques and conditions. See FIG. 6A. In some embodiments, the resulting patterned mandrel layer 236 may have an hourglass shape, depending on the etching techniques and conditions. See FIG. 6B. Embodiments consistent with those depicted in FIGS. 6A and 6B are otherwise identical to FIG. 6. The new width w₂′ of the openings 151 may be between about 200 and 550 Å, such as about 400 Å.

As a result of the etch widening the opening 151, the height-to-width ratio may be reduced from the height-to-width ratio h₂:w₂ to the height-to-width ratio h₂:w₂′. The height-to-width ratio h₂:w₂′ may be between about 0.6 and 2.5, such as about 1.3. Because the height-to-width aspect ratio has been reduced in the patterned mandrel layer 236, the wiggle in the lines that will result in the subsequent etching of the target layer 28 is reduced, discussed below with respect to FIG. 11. In some embodiments, each of the etchings described above with respect to FIGS. 1-6B can be performed in the same etching chamber without removing the device 100 between intermediate steps.

Referring to FIG. 7, following the etching of the patterned mandrel layer 236, the bottom layer 138 may be removed by an ashing process. In a SADP process a spacer material 254 may be deposited over the patterned mandrel layer 236. The spacer material may be a suitable oxide or nitride insulating or dielectric material which is deposited using a deposition technique suitable to form a substantially conformal layer (for example, such that the horizontal portions and vertical portions of the spacer layer 254 vary by 25% or less). Such deposition techniques may include, for example, PECVD, HDPCVD, ALD, CVD, LPCVD, PVD, and the like.

Next, as illustrated in FIG. 8, the spacer layer 254 may be anisotropically etched using a suitable technique to remove horizontal portions of the spacer material, resulting in self-aligned spacer mask 354. The openings 252 represent the openings between mandrels to be etched. In some embodiments, the width of the openings 252 may be between about 80 and 250 Å, such as about 150 Å.

Next, as illustrated in FIG. 9, the mandrels in patterned mandrel layer 236 may be removed to create further openings (such as openings 58) between the spacers of spacer mask 354. Next, mask layer 34 is etched using the self-aligned spacer mask 354 as an etching mask, so that the pattern of self-aligned spacer mask 354 is transferred to mask layer 34 to create a patterned mask layer 134, which may also be referred to as mask layer 134. The patterned mask layer 134 has openings 57 which have been extended from openings 352 and openings 58 which have been extended from the openings resulting from the removal of the patterned mandrels 236. The etching of patterned mask layer 134 may be performed by any suitable technique, such as by a wet or dry etch selective to the material of mask 34. In some embodiments, the etching of patterned mask layer 134 may consume the self-aligned spacer mask 354.

Referring to FIG. 10, following the etching of the mask layer 134, mask layer 134 is used to pattern mask layer 32 to form patterned mask layer 132. Mask layer 32 is etched using the patterned mask layer 134 as an etching mask, so that the pattern of mask layer 134 is transferred to mask layer 32 to form patterned maks layer 132. Patterned mask layer 132 has openings 60 which have been extended from openings 57 and 58. The etchant and etching technique used can be selective to the material of patterned mask layer 132.

In FIG. 11, the patterned mask layer 132 is used as an etching mask to progressively transfer the pattern of patterned mask layer 132 to the underlying mask 30, low-k dielectric target layer 28, and etch stop layer 26 by etching each layer in turn, using one or more of the previous layers as a mask. Openings 62 are formed by extending openings 60 into the underlying layers corresponding to openings to be filled with metal lines and vias. In some embodiments, prior to using mask 132 as a mask in etching the underlying layers, the remaining portions of patterned mask layer 134 may be removed by a separate process. In some embodiments, the remaining portions of patterned mask layer 134 may be removed simultaneously with etching mask 30. The patterned target layer 128 and patterned etch stop layer 126 may be etched using a suitable etching technique such as a wet or dry etch using an appropriate etchant which is selective to the respective materials to be etched. In particular, target layer 128 may be etched using a plasma or RIE anisotropic etch using etch stop layer 26 as an etch stop so that the widths of the resulting trenches are relatively uniform within process variations. Then, in a subsequent process, etch stop layer 26 (e.g., 26A and 26B) may be etched using the target layer 128, patterned hard mask 30, or metal hard mask 132 as a mask to expose the metal features 24. The openings formed in the target layer 128 may include trenches and/or vias. For example, vias may reach the exposed metal features 24, while trenches may be formed to have a bottom which is between the topmost surface of the target layer 128 and the bottommost surface of the target layer 128.

As a result of the lower aspect ratio of the top layer 142 of the tri-layer and subsequent widening of the openings 151 in the patterned mandrel layer 236, the patterned mandrel layer 236 forms mandrels with substantially straight (non-wiggly) sidewalls, in a top down view, which result in a self-aligned spacer mask 354 which also have substantially straight sidewalls as well as the subsequent openings formed therein.

FIG. 11 also illustrates the formation of conductive vias 64A, 64B, and 64C (collectively referred to as vias 64) in openings in the target layer 28 (of FIG. 10). Conductive lines 66A, 66B, and 66C (collectively referred to as lines 66) are also formed in the trenches of target layer 28. Vias 64 and conductive lines 66 may include conductive liners 68, which may be diffusion barrier layers, adhesion layers, and/or the like. Liners 68 may be formed of titanium, titanium nitride, tantalum, tantalum nitride, or other alternatives. The inner regions of conductive lines 66 and vias 64 include a conductive material such as copper, a copper alloy, silver, gold, tungsten, aluminum, or the like. In accordance with some embodiments, the formation of vias 64 and conductive lines 66 includes performing a blanket deposition to form liner 68, depositing a thin seed layer of copper or copper alloy over the liner, and filling the rest of the openings with metallic material, for example, through electro-plating, electro-less plating, deposition, or the like. A planarization such as Chemical Mechanical Planarization (CMP) is then performed to level the surface of conductive lines 66, and to remove excess conductive materials from the top surface of dielectric layer 128. Mask layer 30 (FIG. 10) may be removed in the planarization or etched after the planarization. The cross-sectional view of FIG. 11 may be, for example, along the line A-A of FIG. 22.

In subsequent steps, an additional etch stop layer (not shown) may be formed, and more low-k dielectric layers, metal lines, and vias (not shown) may be formed over the additional etch stop layer. The process steps and resulting structures may be similar to what are shown in FIGS. 1 through 11.

FIGS. 12 through 21 illustrate cross-sectional views of intermediate stages in the formation of features in a target layer in accordance with some embodiments using a double patterning process. It should be understood that the process described in these steps can be altered to use a triple, quadruple, etc. patterning process. Likewise, it should be understood that the process described in these steps can be used in a single patterning process. The process described is a double patterning double etching (2P2E) process, however, it should be understood that it can be readily modified to include a double patterning single etching technique (2P1E) and other similar techniques, e.g. 3P3E, 3P1E, etc. These techniques are considered to be within the scope of this disclosure.

FIG. 12 illustrates an intermediate step in the production of a semiconductor device 100. The layers included correspond to the layers discussed above with respect to FIG. 1. It should be noted that the structure illustrated in FIG. 12 does not include a mandrel layer (mandrel layer 36 of FIG. 1), but in some embodiments, a similar layer made of the same or similar materials (e.g., amorphous silicon) is included as the mask layer used in the double patterning technique. In some embodiments, such as in the description that follows, mask layer 34 serves as the mask layer which will be double patterned for patterning lines in target layer 28.

After the upper layer 42 is formed, upper layer 42 is patterned as illustrated in FIG. 12 using an acceptable photolithography technique. The patterned upper layer 42 includes openings 44 therein. In a top view of device 100, openings 44 may have shapes such as strips, round vias, or conductive patterns. Each of the openings 44 has a height-to-width ratio, h₁:w₁. In some embodiments, the height h₁ of the openings 44 corresponds to the thickness of the top layer 42 and the width w₁ of the openings 44 depends on the photolithography technique used to pattern the top layer 42. The width w₁ of the openings 44 may be between about 180 and 450 Å, such as about 300 Å. Other widths for the openings 44 can be used.

Next, referring to FIG. 13, in order to reduce the height-to-width ratio of the openings 44, the thickness of the upper layer 42 (and corresponding height h₁ of the openings 44 of FIG. 12) is reduced to a height h₁′. Techniques may correspond to those discussed above with respect to FIG. 2. The reduced height-to-width ratio, h₁′: w₁, may be between about 0.5 and 2.0, such as about 1.0. In some embodiments, the width w₁ may be changed to a width w₁′, for example, if the openings 44 of FIG. 12 are widened in the same process which reduces the height of the upper layer 42. In such embodiments, the resulting height-to-width ratio h₁′:w₁′ may be reduced over the ratio h₁:w₁ by an even greater extent.

Next, referring to FIG. 14, middle layer 40 is etched to form patterned middle layer 140, which may also be referred to as middle layer 140. Middle layer 40 is etched using the patterned upper layer 142 (FIG. 13) as an etching mask, so that the pattern of upper layer 142 is transferred to middle layer 40 to create patterned middle layer 140. During the patterning of middle layer 140, upper layer 142 may be partially, or entirely, consumed. Etching the middle layer 40 may result in openings in the middle layer 140 which have been extended from openings 144. Any suitable etching technique may be used, such as a wet or dry etch using an etchant which is selective to the middle layer 140 material.

Next, the bottom layer 38 is then etched to form patterned bottom layer 138, which may also be referred to as bottom layer 138. Bottom layer 38 is etched using the middle layer 140 as an etching mask, so that the pattern of middle layer 140 is transferred to bottom layer 38 to create a patterned bottom layer 138. The bottom layer 138 has openings 48 which have been extended from openings 144 (FIG. 13). Upper layer 142 will also be fully consumed during the patterning of bottom layer 38 if it has not been fully consumed in the patterning of middle layer 140. The patterning of bottom layer 38 results in patterned bottom layer 138. Openings 48 may be tapered or may have vertical sidewalls, within process variations. Etching techniques and conditions may include those discussed above with respect to FIG. 4 and are not repeated.

FIG. 15 illustrates an anisotropic etching of mask layer 34 of FIG. 14 to form patterned mask layer 134, which may also be referred to as mask layer 134. Mask layer 34 is etched using the patterned bottom layer 138 as an etching mask, so that the pattern of bottom layer 138 is transferred to mask layer 34 to create a patterned mask layer 134. The mask layer 134 has openings 50 which have been extended from openings 48 (FIG. 14). The etching technique may include a dry etch using a suitable etchant. Mask layer 32 under the patterned mask layer 134 may serve as an etch stop layer for the etching through of the material of patterned mask layer 134. Openings 51 are a portion of the openings 50 in the patterned mask layer 134 which have a height h₂ and width w₂, where the height h₂ corresponds to the thickness of the patterned mask layer 134 and the width w₂ corresponds to the width w₁, being approximately equal to the width w₁ or w₁′, within process variations. A resulting ratio of the height-to-width, h₂:w₂, may be about 0.8 to about 3.0, such as about 1.6.

Referring to FIG. 15A, in some embodiments, the openings 51 may be widened into the openings 151 by etching the mask layer 134 into the modified mask layer 234 which may also be referred to as mask layer 234. The openings 151 may be widened to have a width w₂′ to reduce the height-to-width ratio from h₂:w₂ to h₂:w₂′.

The etching of mask layer 34 of FIG. 15 or FIG. 15A is a first patterning and etching of the mask layer 134 or 234. A second patterning of the mask layer 134 or 234 may also be performed. In some embodiments, each of the etching processes described above with respect to FIGS. 12-15 can be performed in the same etching chamber without removing the device 100 between intermediate steps.

Referring to FIG. 16, the bottom layer 138 of the tri-layer mask is removed and a new tri-layer mask comprising a bottom layer 52, middle layer 54, and top layer 56 is formed over the first patterned mask layer 134. It should be noted that a portion of the bottom layer 52 fills the openings 50 (see FIG. 15) which were formed in the first patterning of the mask layer 134. It should also be noted that the process described for the second patterning can be performed on the structure resulting from FIG. 15A. For the sake of simplicity, the following discussion will refer to the structure in FIG. 15 (except where noted), however, it should be understood that the structure from FIG. 15A could be substituted as appropriate in the following processes.

Still referring to FIG. 16, after the upper layer 56 is formed, upper layer 56 is patterned using an acceptable photolithography technique. The patterned upper layer 56 includes openings 70 therein. In a top view of device 100, openings 70 may have shapes such as strips, round vias, or conductive patterns. Each of the openings 70 has a height-to-width ratio, h₃:w₃. In some embodiments, the height h₃ of the openings 70 corresponds to the thickness of the top layer 56 and the width w₃ of the openings 70 depends on the photolithography technique used to pattern the top layer 56. The width w₃ of the openings 70 may be of the same or similar dimensions to the width w₁ of the openings 44 of FIG. 12, discussed above.

Next, referring to FIG. 17, in order to reduce the height-to-width ratio of the openings 70, the thickness of the upper layer 56 (and corresponding height h₃ of the openings 70 of FIG. 16) is reduced to a height h₃′ in upper layer 156. Techniques may correspond to those discussed above with respect to FIG. 2. A corresponding height of the openings 70 is reduced to create openings 170. The reduced height-to-width ratio, h₃′:w₃, may be between about 0.6 and 2.5, such as about 1.3. In some embodiments, the width w₃ may be changed to a width w₃′, for example, if the openings 70 of FIG. 16 are also widened in the same process which reduces the height of the upper layer 56. In such embodiments, the resulting height-to-width ratio h₃′:w₃′ of openings 170 may be reduced over the ratio h₃:w₃ by an even greater extent.

Next, referring to FIG. 18, middle layer 54 is etched to form patterned middle layer (not shown), which may also be referred to as middle layer. Middle layer 54 is etched using the patterned upper layer 156 (FIG. 17) as an etching mask, so that the pattern of upper layer 156 is transferred to middle layer 54 to create patterned middle layer. During the patterning of middle layer 54, upper layer 156 may be partially, or entirely, consumed. Etching the middle layer 54 may result in openings in the middle layer 154 which have been extended from openings 170. Any suitable etching technique may be used, such as a wet or dry etch using an etchant which is selective to the middle layer 54 material.

Next, the bottom layer 52 is then etched to form patterned bottom layer 152, which may also be referred to as bottom layer 152. Bottom layer 52 is etched using the patterned middle layer as an etching mask, so that the pattern of the patterned middle layer is transferred to bottom layer 52 to create a patterned bottom layer 152. The bottom layer 152 has openings 72 which have been extended from openings 170 (FIG. 17). Upper layer 156 will also be fully consumed during the patterning of bottom layer 52 if it has not been fully consumed in the patterning of middle layer 54. The patterning of bottom layer 52 results in patterned bottom layer 152. Openings 72 may be tapered or may have vertical sidewalls, within process variations. Etching techniques and conditions may include those discussed above with respect to FIG. 4 and are not repeated.

FIG. 19 illustrates an anisotropic etching of mask layer 134 of FIG. 15 (or mask layer 234 of FIG. 15A) to form double patterned mask layer 334, which may also be referred to as mask layer 334. Mask layer 134 is etched using the patterned bottom layer 152 as an etching mask, so that the pattern of bottom layer 152 is transferred to mask layer 134 to create a patterned mask layer 334. The mask layer 334 has openings 74 which have been extended from openings 72 (FIG. 18). The etching technique may include a dry etch using a suitable etchant. Mask layer 32 under the double patterned mask layer 334 may serve as an etch stop layer for the etching through of the material of double patterned mask layer 334. Openings 75 are portions of the openings 74 in the double patterned mask layer 334 that have a height h₄ and width w₄, where the height h₄ corresponds to the thickness of the layer 334 and the width w₄ corresponds to the width w₃, being approximately equal to the width w₃ or w₃′, within process variations. A resulting ratio of the height-to-width, h₄:w₄, may be about 0.8 to about 3.0, such as about 1.6.

Referring to FIG. 19A, in some embodiments, the openings 75 may be widened into the openings 175 by etching the mask layer 334 into the modified mask layer 434 which may also be referred to as mask layer 434. The openings 175 may be widened to have a width w₄′ to reduce the height-to-width ratio from h₄:w₄ to h₄:w₄′. In embodiments where a first widening in the layer 134 was performed to produce layer 234 (see FIG. 15A), each of the remaining portions of the mask layer 434 will then have been thinned from each side.

Referring to FIG. 19B, the bottom layer 152 of the tri-layer mask has been removed. Removing the bottom layer 152 of the tri-layer mask exposes the first patterned openings 50 (FIG. 15). Subsequently, FIG. 19B illustrates that in some embodiments the mask layer 334 or 434 may be reduced in thickness to provide openings 78 (from the second patterning openings 75 (FIG. 19) or 175 (FIG. 19A)) and openings 80 (from the first patterning openings 51 (FIG. 15 or 151 (FIG. 15A)), having a new height h₄′. The reduction of the thickness of the mask layer 334 or 434 to produce oxide layer 534 may result in a further reduced height-to-width ratio of the openings 78 and openings 80. The height-to-width ratio may be reduced for the openings 78 from h₄:w₄ (or w₄′) to h₄′:w₄ (or w₄′). A resulting ratio of the height-to-width, h₄′:w₄ (or w₄′), may be about 0.4 to about 2.5, such as about 0.8. The height-to-width ratio may be reduced for the openings 80 from h₂:w₂ (or w₂′) (see FIG. 15 or FIG. 15A) to h₄′:w₂ (or w₂′). A resulting ratio of the height-to-width, h₄′:w₂ (or w₂′), may be about 0.4 to about 2.5, such as about 0.8.

The reduced thickness mask layer 534 may be produced by any acceptable technique, including for example, an anisotropic etch with an etchant selective to the material of layer 534.

Referring now to FIG. 19C, in some embodiments the mask layer 634 may be produced which has both a reduced thickness and widened openings. The process illustrated by FIG. 19C may be performed following the process at FIG. 19, FIG. 19A, or FIG. 19B. In other words, embodiments which utilize the process illustrated by FIG. 19C may be combined with the embodiments which utilize the process illustrated by FIG. 19A or FIG. 19B, but such combination is not required. The bottom layer 152 of the tri-layer mask (see, e.g., FIG. 19) has been removed, exposing the first patterned openings 50 (FIG. 15) which correspond to the openings 80. Subsequently, the openings 78 and openings 80 may be widened to width w₅ by performing a wet etch to remove material from the top and sidewalls of the double patterned mask layer 334 (or 434 or 534). The etching also reduces the thickness of the double patterned mask layer 334 which shortens the openings 78 and 80. The height-to-width ratio may be reduced for the openings 78 from h₄:w₄ (or w₄′) to h₄′:w₅. A resulting ratio of the height-to-width, h₄′:w₅, may be about 0.4 to about 2.5, such as about 0.8. The height-to-width ratio may be reduced for the openings 80 from h₂:w₂ (or w₂′) (see FIG. 15 or FIG. 15A) to h₄′:w₅. A resulting ratio of the height-to-width, h₄′:w₅, may be about 0.4 to about 2.5, such as about 0.8.

In some embodiments, the process of FIG. 19C can be followed by the process of FIG. 19B to further reduce the thickness of the double patterned mask layer 634.

Referring to FIG. 20, following the etching of the double patterned mask layer 334 (or 434 or 534, or 634), mask layer 334 is used to pattern mask layer 32 to form patterned mask layer 132, which may also be referred to as mask layer 132. Mask layer 32 is etched using the double patterned mask layer 334 as an etching mask, so that the pattern of the double patterned mask layer 334 is transferred to mask layer 32 to create a patterned mask layer 132. The mask layer 132 has openings 82 (resulting from the second patterning) extending from openings 78 and openings 84 (resulting from the first patterning) extending from openings 80 in mask layer 132. The etchant and etching technique used can be selective to the mask layer 132.

In FIG. 21, the patterned mask layer 132 is used as an etching mask to progressively transfer the pattern of patterned mask layer 132 to the underlying mask 30, low-k dielectric target layer 28, and etch stop layer 26 by etching each layer in turn, using one or more of the previous layers as a mask. Openings 62 are formed by extending openings 82 and 84 into the underlying layers corresponding to openings to be filled with metal lines and vias. In some embodiments, prior to using mask 132 as a mask in etching the underlying layers, the remaining portions of double patterned mask layer 334 may be removed by a separate process. In some embodiments, the remaining portions of double patterned mask layer 334 may be removed simultaneously with etching mask layer 30. The target layer 128 and etch stop layer 126 may be etched using a suitable etching technique such as a wet or dry etch using an appropriate etchant which is selective to the respective materials to be etched. In particular, target layer 128 may be etched using a plasma or RIE anisotropic etch using etch stop layer 26 as an etch stop so that the widths of the resulting trenches are relatively uniform within process variations. Then, in a subsequent process, etch stop layer 26 (e.g., 26A and 26B) may be etched using the target layer 128, patterned hard mask 30, or metal hard mask 132 as a mask to expose the metal features 24. The openings formed in the target layer 128 may include trenches and/or vias. For example, vias may reach the exposed metal features 24, while trenches may be formed to have a bottom which is between the topmost surface of the target layer 128 and the bottommost surface of the target layer 128.

As a result of the lower aspect ratio of the top layer 142 (FIG. 12) and top layer 156 (FIG. 17) of the tri-layer and subsequent widening of the openings in the double patterned oxide layer 334, the double patterned oxide layer 334 can have substantially straight (non-wiggly) sidewalls, in a top down view, which result in the subsequent openings formed in the target layer 28 likewise having substantially straight sidewalls. In some embodiments, each of the etchings described above with respect to FIGS. 16-21 can be performed in the same etching chamber without removing the device 100 between intermediate steps.

FIG. 21 also illustrates the formation of conductive vias 64A, 64B, and 64C (collectively referred to as vias 64) in openings in the target layer 28 (of FIG. 20). These features can be formed using materials and processes similar to those discussed above with respect to FIG. 11, which are not repeated. The cross-sectional view of FIG. 21 may be, for example, along the line A-A of FIG. 22.

In subsequent steps, an additional dielectric ESL layer (not shown) may be formed, and more low-k dielectric layers, metal lines, and vias (not shown) may be formed over the additional dielectric ESL layer. The process steps and resulting structures may be similar to what are shown in FIGS. 12 through 21.

FIG. 22 illustrates a top down view of the conductive lines 66 following the planarization discussed with reference to FIG. 11 and FIG. 21. The wiggle characteristic of a portion of the line 66 may be illustrated by equation 1. Line wiggle=√{square root over (½(LER _(right))²+½(LER _(left))²−¼(LWR)²)}  (eq. 1)

In equation 1, LER_(right) corresponds to a measurement of line edge roughness on one side (i.e., the right side) of the line, LER_(left) corresponds to a measurement of line edge roughness on the other side (i.e., the left side) of the line, and LWR corresponds to a measurement of line width roughness (variation or unevenness), within a section of the line 66. LWR is determined based on the combined measurements LW1 through LWn measured in one or more segments of the line 66. LWR is a statistical measure of the variation in the width of the line at multiple points along the length of the one or more line segments. LWR represents high frequency variation of the line.

LER is determined based on the combined measurements LE1 through LEn measured in the one or more segments of the line. These measurements are taken for the left side (LER_(left)) and right side (LER_(right)) of the line for each of the one or more segments of the line. The value for each measurement LE1 through LEn is a variation from a reference line 90 near the edge of the metal line. In some embodiments, reference line 90 may be a line of best fit or average line for the edge profile. LER represents both high frequency and low frequency variations of the edges of the line. Measurements used for LWR and LER calculations can be taken in a top down view of the line 66, for example by analyzing a top-view image from a critical dimension scanning electron microscope (CD-SEM). The statistical measures for determining LWR and LER from raw measurements LWx and LEx, respectively, can be calculated using known techniques. For example, LWR and LER may be selected to be the 1-sigma (σ) standard deviation values for the respective measurements. Other measures may be used. Eq. 1 for line wiggle is a mathematical combination of the LWR and LER measurements representing multiple characteristic factors for the line wiggling.

Embodiments can produce a line 66 having a line wiggle between about 0.7 and about 1.3, such as about 1.1, as determined by Eq. 1. In testing, using embodiments as described above, line wiggling was reduced from a value greater than 2.0 to 1.3. In another example, line wiggling was reduced from a value of 1.4 to a value of 1.1. Line wiggling can be reduced by about 20 to 60%, such as about 40% using embodiments described above. In addition to such objective measurements, subjectively, low frequency distortion of the metal lines are reduced using embodiments described above as viewed, for example, in a top down CD-SEM image.

FIGS. 23 and 24 illustrate patterning of a substrate in accordance with some embodiments. FIG. 23 illustrates a substrate 10 which will be subsequently patterned to form fins as part of one or more fin field-effect transistors (FinFETs). The layers presented in FIG. 23 may be the same or similar to those depicted in FIG. 1 or FIG. 12, except that no active devices are yet formed in the substrate 10. The steps to pattern the patterned mask layer 36 (FIG. 1) or patterned mask layer 34 (FIG. 12) may follow as described above with respect to FIGS. 1-6B or FIGS. 12-19C. In some embodiments, one or more of mask layer 30, mask layer 32, and mask layer 34 may be omitted. In some embodiments, the semiconductor substrate 10 may be considered to replace layer 36 (FIG. 1) or layer 34 (FIG. 12), omitting the following layers. The mask layer 30, mask layer 32, and mask layer 34 may be patterned using processes and materials such as described above with respect to FIGS. 7-9 or FIGS. 20-21.

Referring to FIG. 24, mask layer 130 (see descriptions accompanying FIGS. 10-11 or FIGS. 20-21), may be used to pattern the substrate 10 to form semiconductor strips 110. As a result of using the process described above, the semiconductor strips 110 may be formed such that they have reduced wiggle.

Following the formation of semiconductor strips 110, the semiconductor strips 110 may be used to form a FinFET device, such as transistor 11 (FIG. 1). In particular, a gate structure, such as gate electrode 12 and gate spacers 13 of FIG. 1, may be formed over the semiconductor strips 110, perpendicular to the direction of the semiconductor strips 110. Source/drain regions, such as source/drain regions 14 of FIG. 1, may be formed adjacent to the gate structure. Transistor contacts 15 (gate contact and source/drain contacts) may be formed to contact the transistor 11.

Embodiments disclosed herein provide a way to create metal lines in devices at fine pitches having less wiggle than in other techniques. Eliminating or reducing wiggle provides for more reliable interconnects at finer pitch widths.

One embodiment includes a method which includes forming a first patterning layer over a metal feature. A first mask layer is deposited over the first patterning layer. Next, the first mask layer is patterned to form a first set of one or more openings therein. The first mask layer is then thinned. The pattern of the first mask layer is transferred to the first patterning layer to form a second set of one or more openings therein. The first patterning layer is etched to widen the second set of one or more openings.

Another embodiment includes a method which includes forming a dielectric layer over a substrate, where the substrate contains one or more active devices. A first patterning layer is formed over the dielectric layer. A first tri-layer is formed over the first patterning layer, where the first tri-layer includes a top layer of a first material, a middle layer of a second material, and a bottom layer of a third material. The top layer is patterned to form a first set of openings and then the top layer is thinned to decrease a height-to-width ratio of the first set of openings. The transferring the pattern of the top layer is transferred to the middle layer to form a second set of openings, and the pattern of the middle layer is transferred to the bottom layer to form a third set of openings. The first patterning layer is etched through the third set of openings to form a fourth set of openings, which are then widened.

Another embodiment is a device which includes a substrate having one or more active devices formed therein and a contact coupled to a first active device of the one or more active devices. The device also includes an interconnect over the contact, where the interconnect includes a metal line coupled to the contact. The metal line has a first portion which overlaps the contact, where the first portion of the metal line has a wiggle characteristic. The wiggle characteristic of the first portion of the metal line is calculated by √{square root over (½(LER_(right))²+½(LER_(left))²−¼(LWR)²)}, where LER_(right) corresponds to a measurement of line edge roughness of a right side of the first portion of the metal line, LER_(left) corresponds to a measurement of line edge roughness of a left side of the first portion of the metal line, and LWR corresponds to a measurement of line width roughness of the first portion of the metal line, wherein the wiggle characteristic is between 0.7 and 1.3.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method, comprising: forming a first patterning layer over a metal feature; depositing a first mask layer over the first patterning layer; depositing a second mask layer interposed between the first patterning layer and the first mask layer; patterning the first mask layer to form a first set of one or more openings therein; thinning the first mask layer to form a pattern of thinned first mask layer; after thinning the first mask layer, transferring the pattern of the thinned first mask layer to the second mask layer to form a second set of one or more openings and to form a pattern of the second mask layer; transferring the pattern of the second mask layer to the first patterning layer to form a third set of one or more openings therein; and etching the first patterning layer to widen the third set of one or more openings without widening the second set of one or more openings, wherein the third set of one or more openings is widened while the second mask layer is over the first patterning layer.
 2. The method of claim 1, wherein the first patterning layer is a silicon layer.
 3. The method of claim 2, further comprising: after widening the third set of one or more openings, depositing a spacer material over the first patterning layer; anisotropically etching the spacer material to form a spacer pattern layer; removing the first patterning layer; and etching a target layer based on the spacer pattern layer, the target layer being interposed between the first patterning layer and the metal feature.
 4. The method of claim 3, wherein etching the target layer forms a fourth set of one or more openings therein, and the method further comprises: depositing a conductive material in the fourth set of one or more openings of the target layer, wherein the conductive material is coupled to the metal feature.
 5. The method of claim 1, wherein the first patterning layer is an oxide layer.
 6. The method of claim 5, further comprising: thinning the first patterning layer.
 7. The method of claim 5, further comprising: removing the second mask layer; depositing a third mask layer over the first patterning layer; patterning the third mask layer to form a fourth set of one or more openings therein; thinning the third mask layer to form a pattern of thinned third mask layer; transferring the pattern of the thinned third mask layer to the first patterning layer to form a fifth set of one or more openings therein; and etching a target layer based on the widened third set of one or more openings and fifth set of one or more openings in the first patterning layer.
 8. The method of claim 7, wherein etching the target layer forms a sixth set of one or more openings therein, and the method further comprises: depositing a conductive material in the sixth set of one or more openings of the target layer, wherein the conductive material is coupled to the metal feature.
 9. The method of claim 8, wherein prior to etching the target layer, thinning the first patterning layer.
 10. The method of claim 1, further comprising: after thinning the first mask layer, etching a third mask layer interposed between the second mask layer and the first mask layer.
 11. The method of claim 1, wherein etching the first patterning layer to widen the third set of one or more openings is performed without etching through a layer directly underlying the first patterning layer.
 12. A method, comprising: forming a dielectric layer over a substrate, wherein the substrate contains one or more active devices; forming a first patterning layer over the dielectric layer; forming a first tri-layer over the first patterning layer, the first tri-layer comprising a top layer of a first material, a middle layer of a second material, and a bottom layer of a third material; patterning the top layer to form a first set of openings and a first pattern of the top layer; thinning the top layer to decrease a height-to-width ratio of the first set of openings; transferring the first pattern of the top layer to the middle layer to form a second set of openings and a second pattern of the middle layer; transferring the second pattern of the middle layer to the bottom layer to form a third set of openings; etching the first patterning layer through the third set of openings to form a fourth set of openings; and while the bottom layer is over the first patterning layer, etching the first patterning layer through the third set of openings to widen the fourth set of openings without widening the third set of openings, wherein a layer directly underlying the first patterning layer prevents etching the dielectric layer while widening the fourth set of openings.
 13. The method of claim 12, wherein the first patterning layer is a silicon layer, wherein the method further comprises: after widening the fourth set of openings, depositing a spacer layer over the first patterning layer; removing horizontal portions of the spacer layer; removing the first patterning layer; and etching the dielectric layer using vertical portions of the spacer layer as a mask to form a fifth set of openings therein.
 14. The method of claim 13, further comprising depositing a conductive material in the fifth set of openings, wherein the conductive material is coupled to the one or more active devices.
 15. The method of claim 12, wherein the first patterning layer is an oxide layer.
 16. The method of claim 15, further comprising: following etching the first patterning layer to form the fourth set of openings, depositing a second tri-layer over the first patterning layer, the second tri-layer having a same structure as the first tri-layer; patterning the second tri-layer and forming a fifth set openings in a bottom layer of the second tri-layer; and etching the first patterning layer through the fifth set of openings formed in the bottom layer of the second tri-layer to form a sixth set of openings therein.
 17. The method of claim 16, further comprising: following forming the sixth set of openings in the first patterning layer, thinning the first patterning layer.
 18. The method of claim 16, further comprising: etching the dielectric layer based on the widened fourth set of openings and the sixth set of openings in the first patterning layer to form a seventh set of openings; and depositing a conductive material in the seventh set of openings, wherein the conductive material is coupled to the one or more active devices.
 19. A method, comprising: patterning a first mask layer to form first openings therein; transferring a first pattern of the first openings to a second mask layer underlying the first mask layer to form second openings in the second mask layer; transferring a second pattern of the second openings to a mandrel layer underlying the second mask layer to form third openings in the mandrel layer; while the second mask layer is over the mandrel layer, etching the mandrel layer to widen the third openings without widening the second openings and without etching through any layers directly underlying the mandrel layer; removing the second mask layer; forming a spacer mask in the third openings of the mandrel layer; and etching a target layer underlying the spacer mask based on a third pattern of the spacer mask.
 20. The method of claim 19, further comprising: anisotropically etching the spacer mask to form the third pattern; removing the mandrel layer; and forming conductive features in the target layer electrically coupled to active devices in an underlying substrate. 